Indirectly heated dispenser cathode for electrical discharge vessels



Feb. l0, 1970 H. KA'rz INDIRECTLY HEATED DISPENSER CATHODE FORELECTRICAL DISCHARGE VESSELS Filed April 3, 1968 [NVE/WOR. #6L/w07 /szrma-f @w ra/W ATTORNEYS United States Patent O INDIRECTLY HEATEDDISPENSER CATHODE FOR ELECTRICAL DISCHARGE VESSELS Helmut Katz, Munich,Germany, assignor to Siemens Aktiengesellschaft, a corporation ofGermany Filed Apr. 3, 1968, Ser. No. 718,410 Claims priority,application Germany, Apr. 10, 1967, S 109,263 Int. Cl. H01j 1/14, 19/06U.S. Cl. 313-346 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THEINVENTION Field of the invention The invention relates to an indirectlyheated dispenser cathode in which a heater is energized by a DC source.

Description of the prior art Presently indirectly heated dispensercathodes such as used in travelling wave tubes and disk seal tube worksatisfactory with alternating current, but upon the application of adirect current voltage, electrolytic decomposition occurs during theoperation in the insulating material such as aluminum oxide which willresult in leakage current between the heater and the cathode shell, thusleading to short circuits between the heater and the cathode.

SUMMARY OF THE INVENTION The present invention abrogates thedisadvantages of the prior art by surrounding the indirectly heatedcathode with a ceramic cylinder which is spaced between insulationmaterial around the heaterV and the thin metallic shield which forms theouter shell of the cathode. The ceramic shielding cylinder which isplaced around the indirectly heated cathode eliminates the electrolyticdecomposition which occurs conventionally in such structures whenenergized by a DC source. Various modifications of the invention arealso disclosed which eliminate electrolytic decomposition effects.

Other objects, features and advantages of the present invention will bereadily apparent from the following detailed description of certainpreferred embodiments thereof taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a sectional view of theindirectly heated dispenser cathode of this invention;

FIGURE 2 is a modification of the dispenser cathode; and

FIGURE 3 is a further modification of the dispenser cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 illustrates anindirectly heated dispenser cathode which has a pair of electrical inputleads 11 and 12 which pass through insulating cylinders 13 and 14 thatextend outwardly from the dispenser cathode 10. Within the cathodestructure the leads 11 and 12 are cov- 3,495,121 Patented Feb. 10, 1970ered with a suitable insulation material 16 which might, for example, bealuminum oxide and are formed into a bifilar coil 15. A pot-shapedsupply container 19 holds the emissive material 21 which when heatedemits electrons. A ceramic cylinder 24 which might, for example, be madeof an oxide ceramic such as aluminum oxide or beryllium oxide isconnected to the supply container 19 by press-fitting over a collar 22or by using conventional soldering technique. The heater coil 15 ismounted within the ceramic cylinder 24 and is encapsulated by an oxidematerial 23 that might be aluminum or beryllium oxide -which fills thespace between the ceramic cylinder 24 and the heater coil 15. A thinfoil cylinder 18 is also attached to the supply container 19 and extendsaround the ceramic shell 24 but is spaced away from it.

The ceramic shell 24 which is spaced between the metallic shell 18 andthe heater 15 allows either alternating or direct current voltage to beapplied to the leads 11 and 12 to heat the heater 15 and undesirableelectrolytic decomposition effects are prevented because of theisolating qualities of the shell 24. As a result, the poten tialdifferences normally present with direct current between the heater andthe cathode shell 18 are eliminated.

Even the potentials which at most amount to the heater voltage whichmight still occur between adjacent turns of the customary bifilar heaterwinding 15 can be eliminated by the modifications shown in FIGURES 2 and3.

FIGURE 2, for example, illustrates a single turn coil heater 31 whichhas a first input lead 27 which passes through an insulating cylinder29. The other end 33 0f the heater end 34 is electrically connected tosupply container 19 which is in turn connected to a foil cylinder 32which is spaced closely adjacent the ceramic cylinder 24 but is spacedfrom shell 18. A second lead 26 passes through an insulating sleeve 28and through the wall of the ceramic cylinder 24 and is electricallyconnected to the end of the foil cylinder 32 adjacent the lead 27 at 36.The foil cylinder 32 in combination with the ceramic cylinder 24improves heat economy of the cathode and eliminates radiation losses.

It is to be particularly noted that the heaters in FIG- URES 2 and 3 aresingle turn heaters wherein the winding extends within the cylinder 24from one end to the other and the return is. through either the shell 32in FIGURE 2 or as shown in FIGURE 3 through the outer conductive shell18. FIGURE 3 illustrates the input leads 26 and 27 which pass throughthe insulating cylinders 28 and 29` which extend from the cathode. Theupper end 41 of the heater 31 has its end 42 connected to the supplycontainer 19. The lead 26 passes through the wall of the ceramiccylinder 24 at 44 and has its end 43 electrically connected to thecylinder 18 of the cathode.

The structure of FIGURE 3 allows the return current to pass through thefoil cylinder 18 between points 42 and 43. Likewise in FIGURE 2 thereturn current passes from points 34 to 36 through the cylinder 32.

Although minor modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

I claim as my invention:

1. An indirectly heated cathode for an electrical discharge vessel thathas a heater and a supply chamber for the supply of emission and whichis sealed by a porous emission material carrier disk and which isattached to a supporting cylinder of metal foil comprising, a ceramiccylinder attached to the supply chamber and contained within saidsupporting cylinder.

2. A cathode as claimed in claim 1 wherein said heater is a bifilarspiral heater.

3. A cathode as claimed in claim 1 wherein said heater is a singleiilament spiral having one end connected to said supply chamber.

4. A cathode as claimed in claim 3 in which an additional metal cylinderis attached to said supply vchamber and is mounted between said ceramiccylinder and said supporting cylinder and said additional metal cylinderserves as a supply lead for said heater.

5. A cathode as claimed in claim 1 wherein said ceramic cylinder isformed of aluminum oxide.

6. A cathode as claimed in claim 1 wherein said ceramic cylinder isformed of beryllium oxide.

7. A cathode as claimed in claim 3 wherein said supporting cylinderserves as a supply lead for said heater.

4 References Cited UNITED STATES PATENTS 2,870,366 1/1959 Vantol 313-346X 3,056,061 9/ 1962 Melsert 313-346 3,421,039 1/1969 Knauer et alB13-346 X FOREIGN PATENTS 1,225,314 2/ 1960 France.

10 JOHN W. HUCKERT, Primary Examiner ANDREW I. JAMES, Assistant ExaminerU.S. Cl. X.R. 313-337, 345

